[SPARK-18719] Add spark.ui.showConsoleProgress to configuration docs

This PR adds `spark.ui.showConsoleProgress` to the configuration docs.

I tested this PR by building the docs locally and confirming that this change shows up as expected.

Relates to #3029.

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #16151 from nchammas/ui-progressbar-doc.

docs/configuration.md

@@ -699,6 +699,15 @@ Apart from these, the following properties are also available, and may be useful
     This is the URL where your proxy is running. This URL is for proxy which is running in front of Spark Master. This is useful when running proxy for authentication e.g. OAuth proxy. Make sure this is a complete URL including scheme (http/https) and port to reach your proxy.
   </td>
 </tr>
+<tr>
+  <td><code>spark.ui.showConsoleProgress</code></td>
+  <td>true</td>
+  <td>
+    Show the progress bar in the console. The progress bar shows the progress of stages
+    that run for longer than 500ms. If multiple stages run at the same time, multiple
+    progress bars will be displayed on the same line.
+  </td>
+</tr>
 <tr>
   <td><code>spark.worker.ui.retainedExecutors</code></td>
   <td>1000</td>